This invention relates in general to a nut for securing a machine component on an external thread and more particularly to a locking nut which may be secured against rotation without changing its axial position, to a bearing assembly including the nut, and to a method of manufacturing the nut.
Locking nuts exist in a variety of configurations for securing machine components to spindles and shafts. One of the more important uses of locking nuts resides in holding bearings on spindles, particularly on spindles at ends of drive and steer axles for large trucks. The typical spindle on one of these axles carries two single row tapered roller bearings which are mounted in opposition, and the bearings in turn carry a hub, enabling it to rotate with minimum friction on the spindle. The inner races or cones of the bearings fit around the spindle, while the outer races or cups fit into the hub. The spindle at its end has a thread over which a nut passes, and the position to which the nut is advanced determines the setting for the bearings. Most automotive bearings are set near a condition known as zero end play, whether it be with a very slight amount of end play or a very slight amount of preload. Too much end play detracts from stability and the hub and wheel may wobble. This in turn produces excessive seal wear. Moreover, excessive end play causes the load zone in each of the bearings to concentrate at a few rollers, and this may shorten the life of the bearing. Excessive preload, or the other hand, imparts more force to the bearings and may cause the bearings to fail early.
While a variety of nuts exist for holding bearings in place on spindles, perhaps the most common is the jam nut arrangement. This basically consists of two nuts, one threaded up behind the other. Indeed, the first nut is turned down against the inner race of the outboard bearing until a desired setting is obtained. Any of several procedures are available for determining the setting. Perhaps the most basic is simply by feel. Then one can monitor the torque. One can also monitor torque and back off of a prescribed amount which is usually specified in terms of nut rotation. In any event, the first nut brings the bearing to a desired setting, and when that setting is achieved the thread of the first nut lies against the inboard flanks of the thread on the spindle, that is to say against the flanks which are presented toward the bearing. Next, with the first nut held against rotation, the second nut is advanced over the spindle and turned down tightly against the first nut, or more likely against a washer interposed between the two nuts. The threads of the second nut likewise bear against the inboard flanks of the spindle thread, and indeed the second nut drives the first nut slightly farther along the spindle--far enough to bring the thread of the first nut against the outboard flanks of the thread on the spindle. This changes the setting of the bearings and one must account for it when establishing the initial setting with the first nut. Thus, the traditional double nut arrangement does not lend itself to much precision.
Single locking nuts exist, and some of these do not change the setting of the bearings. But most single nuts require substantial machine work and are expensive to manufacture. Moreover they do not secure the nut as firmly as required in some applications. Sometimes they remain loose on the external thread, and this subjects them to vibration damage.
The present invention resides in a locking nut which, when secured against rotation, does not change its position along an external thread such as the thread of a spindle or a shaft. As such the nut is ideally suited for setting tapered roller bearings mounted in opposition on a shaft or spindle. The nut in essence includes two rings and some type of fastening device, such as cap screws, for changing the relationship between the rings. When the cap screws are backed off, the nut will turn easily on the external thread. However, when the cap screws are tightened, they deform the secondary ring and in effect jam it with respect to the main ring. The invention also resides in a bearing arrangement including the nut, in the combination of the nut and an external thread, and in a method of manufacturing the nut.